JohnDamascus accepts the phrase "theandric energies" (ie energies = actions) because: "the human part did not energise merely in a human manner, for He was not mere man; nor did the divine part energise only after the manner of God, for He was not simply God, but He was at once God and man." Through the "permeation" or "interchange" of natures, which comes from their "close communion," each action of Christ "manifests" itself as both divine and human. This is how Chalcedonians accept "theandric energies."
The essential passage in the Damascene is:
This, then, the theandric energy makes plain that when God became man, that is when He became incarnate, both His human energy was divine, that is deified, and not without part in His divine energy, and His divine energy was not without part in His human energy, but either was observed in conjunction with the other. Now this manner of speaking is called a periphrasis, viz., when one embraces two things in one statement. For just as in the case of the flaming sword we speak of the cut burn as one, and the burnt cut as one, but still hold that the cut and the burn have different energies and different natures, the burn having the nature of fire and the cut the nature of steel, in the same way also when we speak of one theandric energy of Christ, we understand two distinct energies of His two natures, a divine energy belonging to His divinity, and a human energy belonging to His humanity. http://www.orthodox.net/fathers/exactiii.html#BOOK_III_CHAPTER_XIX
So he admits that there is "one theandric action" or in other words "one composite action." Now this is interesting: I dont think (though I would love to be wrong on this! - so please show me otherwise) he ever admitted that there is one theandric nature or one theandric will. Though he comes close:
When the blessed Dionysius says that Christ exhibited to us some sort of novel theandric energy, he does not do away with the natural energies by saying that one energy resulted from the union of the divine with the human energy: for in the same way we could speak of one new nature resulting from the union of the divine with the human nature.
How come he does not work on this thought in his treatises on the natures and the wills?
I think its because he does not want to make the concession to his opponents. PostChalcedonian theologians admitted one theandric action because they accepted Dionysius as an authority.
This had to be explained without much repercussion elsewhere. The theandric action is interpreted more as a manifestation. But given the bold sentence above, Chalcedonians should also be able to speak about one theandric nature and one theandric will, as composite in some sense.